Templatization

Templatization lets you embed dynamic placeholders in rule node configuration fields so that actual values are substituted from the incoming message at runtime. Instead of hardcoding a device name or location, you write a template like ${deviceName} and the rule engine fills it in when the message is processed.

Syntax

Templates start with a dollar sign ($) followed by a bracketed key name.

Bracket type	Source	Example
Square `$[key]`	Message payload	`$[temperature]`
Curly `${key}`	Message metadata	`${deviceName}`

Dot notation accesses nested payload keys: $[object.property].

Two wildcard templates serialize the entire payload or metadata as a JSON string:

Template	Replaced with
`$[*]`	Full message payload as a JSON string
`${*}`	Full message metadata as a JSON string

Example

Given this incoming message:

Payload

{
  "temperature": 26.5,
  "humidity": 75.2,
  "windSpeed": 26.2,
  "location": "riverside"
}

Metadata

{
  "deviceType": "weather_sensor",
  "deviceName": "weather1",
  "ts": "1685379440000"
}

A REST API URL template in a rule node:

example-base-url.com/report-reading?location=$[location]&deviceName=${deviceName}

Resolves at runtime to:

example-base-url.com/report-reading?location=riverside&deviceName=weather1

Type Behavior

The following table shows what value is returned for each data type in the payload:

Template	Payload value	Extracted result
`$[number]`	`123.45`	`123.45`
`$[string]`	`"text"`	`text`
`$[boolean]`	`true`	`true`
`$[null]`	`null`	`null`
`$[array]`	`[1, 2, 3]`	`$[array]` (unchanged)
`$[object]`	`{ "property": "val" }`	`$[object]` (unchanged)
`$[object.property]`	— nested access	`val`
`$[doesNotExist]`	(key absent)	`$[doesNotExist]` (unchanged)

Notes

Templates can be mixed with plain text: "Fuel tanks are filled to $[fuelLevel]%".
The $[*] wildcard includes all payload fields as a compact JSON string, for example: "Raw data: $[*]" → "Raw data: {"mode":"eco","targetTemp":21,"active":true}".
The ${*} wildcard does the same for metadata.

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